using System.Collections.Generic;
using System.IO;
using System.Text;

namespace CsvLib;

public class CsvParser
{
    private bool _insideString;

    private readonly char _separator;
    private readonly char _quoteChar;
    private readonly char _escapeChar;

    public CsvParser(char separator = ',', char quoteChar = '"', char escapeChar = '\\')
    {
        _separator = separator;
        _quoteChar = quoteChar;
        _escapeChar = escapeChar;
    }

    private List<List<string>> _data = new();

    private List<string>? _currentReg;
    private StringBuilder? _currentCell;

    public List<List<string>> Data
    {
        get { return _data; }
    }

    private void ParseLine(string line)
    {
        _currentReg ??= new List<string>();
        _currentCell ??= new StringBuilder();

        for (int i = 0; i < line.Length; i++)
        {
            char c = line[i];
            if (c == _separator && _insideString == false)
            {
                _currentReg.Add(_currentCell.ToString());
                _currentCell.Clear();
                continue;
            }
            if (c == _quoteChar && _insideString == false)
            {
                _insideString = true;
                continue;
            }
            if (c == _quoteChar && _insideString)
            {
                _insideString = false;
                continue;
            }
            if (c == _escapeChar && _insideString)
            {
                i++;
                if (i == line.Length) { break; }
                c = line[i];
            }

            _currentCell.Append(c);
        }


        if (_insideString)
        {
            _currentCell.Append('\n');
        }
        else
        {
            _currentReg.Add(_currentCell.ToString());
            _currentCell.Clear();
            _data.Add(_currentReg);
            _currentReg = null;
        }
    }

    public void ParseFile(string file, long offset = 0, int count = 0)
    {
        _insideString = false;
        _data = new List<List<string>>();
        _currentReg = null;
        FileStream stream = new(file, FileMode.Open);
        stream.Seek(offset, SeekOrigin.Begin);
        using (StreamReader reader = new(stream, Encoding.Default, true, 4096))
        {
            while (reader.ReadLine() is { } currentLine)
            {
                ParseLine(currentLine);
                if (count > 0 && Data.Count == count)
                {
                    break;
                }
            }
        }
        stream.Close();
    }

}